Mars Science Laboratory (MSL) arms on Opportunity and Spirit both use potentiometers to report robotic arm joint position. A potentiometer is a low-accuracy feedback device.
The MSL arm on Curiosity was the first Mars arm to transition away from potentiometers and implemented resolvers to provide joint position feedback. The system experienced noise issues, and no pre-amp electronics were incorporated because that arm could not support the size and mass of pre-amp electronics available at that time. Without pre-amp electronics, the resolver output position telemetry became unusable. Motor encoders (which did not support joint output sensing) were installed to support joint position knowledge.
The NASA Goddard Flight Telerobotic Servicer (FTS) arms incorporated resolver-based position sensors to report joint position. These arms were planned for use on the International Space Station (ISS), but they were never flown.
The German Aerospace Center (known as DLR) built and demonstrated the Robot Technology Experiment (ROTEX), a small robotic arm which incorporated an early version of joint position sensing, in a Spacelab experimentation rack. DLR's Robotics Component Verification on the ISS (ROKVISS) was a 2-DOF arm which built upon lessons learned from ROTEX, implementing magnetoresistive encoders to report joint position. Both ROTEX and ROKVISS were used in the LEO environment.
The European Robotic Arm (ERA), similar to the Space Station Remote Manipulator System (SSRMS) and JEMSRMS, was a large, relocatable, symmetrical arm built for use on the Russian Multipurpose Laboratory module of the ISS. The ERA will work with the Russian airlock to transfer small payloads directly from inside to outside the ISS. It will be teleoperated by astronauts from inside or outside the ISS. The ERA is designed and assembled by Dutch Space. The ERA joint position is determined from the difference between a joint position set point and the joint position measurements of an optical position sensor. It also uses the difference between a velocity set point and motor velocity position measurement provided by a resolver.